It is well known to those skilled in designing new apparatus for chlorination of molten salts that ever increasing requirements are placed upon elements of the apparatus. First, the elements are to provide a uniform chlorine distribution in the melt along the chlorine path and a complete chlorine utilization. Second, the apparatus elements should be simple in production and reliable in service under aggressive media conditions. These requirements are not so far met adequately in any one of the known apparatus.
In particular, known in the prior art is a chlorination apparatus (see Streletz, H. L. "Magnesium production by electrolysis", "Metallurgizdat", 1962, p. 79) comprising a rectangular shell lined with a refractory material and formed by walls, a bottom and a cover. Electrodes and a gaseous product outlet means are introduced into the shell through the cover. The shell walls are provided with chlorine inlet means, a melt feed inlet means and a chlorinated melt outlet means.
In the known prior art apparatus, the chlorination space is composed of a plurality of chlorination zones separated by partitions and horizontal grates. Molten salts are chlorinated by an interaction of the melt flow fed to the upper portion of the apparatus interior and the chlorine gas forced by a pressure into the lower portion of the apparatus under the grates.
However, such apparatus have complicated constructions and are insufficiently efficient in operation.
Note also that in this device the chlorination process goes on actively only in the vicinity of chlorine inlet means. Dead (stagnation) zones are always formed in the lower portion of the apparatus interior, where the melt does not contact the chlorine, whereby insoluble suspensions are settled, this followed by formation of viscous slurry hereinafter called sludge which should be intermittently removed.
Furthermore, in the known prior art apparatus, the gas distribution grates are made as ceramic plates mounted into the lining on the periphery and having shaped holes for chlorine passage over the entire area.
The gas distribution grates considerably limit the time of continuous operation of the apparatus because of emergency conditions which occur frequently. First, they take place since certain holes in the gas distribution grates are clogged up with the sludge and lining crumbs during the operation. As a result, the chlorine contact with the melt is disturbed. Second, the gas distribution grates are quickly destroyed by hydraulic impacts and vibrations.
In Great Britain Pat. No. 1478864 "Process and Apparatus for Producing Anhydrous Magnesium Chloride", packing of lumps of carbonaceous material uniformly distributed over the entire volume of the chlorination tower are used as gas distribution grates. However, carbonaceous material packing is ultimately overgrown with sludge, necessitating a periodical repair of the chlorination tower and replacement of the packing.
In the patent mentioned hereinabove the construction of the chlorination tower is such that the melt of magnesium chloride salts is pumped through heated pipes to the top of rectangular shell of the chlorination tower packed with a bed of carbonaceous material lumps. At the same time chlorine and oxygen are supplied through a heated pipe to the tower base and fed through the chlorine inlet means in counter-current flow with the melt flowing downward.
The height of the chlorination tower is considerably increased as compared with that of the apparatus discussed hereinabove, thus providing contact between the chlorine and the melt for a longer period of time. However, the chlorine and melt flows may separate owing to the non-uniform sludge settling to the beds of carbonaceous material.
Furthermore, the pump used to produce the melt flow through the chlorination tower and special means employed for recycling the melt extremely complicate the construction of the chlorination apparatus.
It is also important to note that the operation of the apparatus is hampered by the fact that it is necessary to remove periodically the sludge from its chlorination tower, and this, in turn, requires a high labour consumption and additional expenditures.
Also known (cf. USSR Author's Certificate No. 532391) is an apparatus for chlorination of molten magnesium chloride salts, comprising a conical shell lined with a refractory material with a lid, electrodes, a gas distribution grate, chlorine inlet means, a melt feed inlet connection and a chlorinated melt outlet connection. The gas distribution grate is made of beams arranged horizontally one above the other, the longitudinal axes of the beams being displaced with respect to each other. The chlorine inlet means are mounted in the shell walls below the grate in the most narrow, lower portion of the apparatus.
In this construction the contact surface of the chlorine and melt is increased due to the downward tapering of the apparatus interior and, as a result, due to sufficiently high speeds of the gas and the melt in the lower portion of the apparatus as the chlorine is introduced.
Such an apparatus has a considerably simpler construction and a longer service life than the prior art apparatus intended for similar applications. In particular, the design of the grate is more simple.
However, such a construction can be used only in apparatus of a small capacity up to 6 tons, since any increase in the apparatus diameter would lead to disturbances in the uniform chlorine distribution in the melt bulk, to an excessive increase in mechanical loads acting on construction elements, and to a decrease in reliability of fastening the beams forming the grate.
It is important to note than an attempt was made to overcome difficulties arising in course of apparatus operation owing to the use of gas distribution grates by changing their construction and this attempt led to negligible results. Grates made of beams are more stable to mechanical loads and especially simpler in construction, but the grate utilization itself hinders the melt in the entire volume of apparatus chlorination space to be involved into the melt circulation. As a result, the sludge is also settled on the bottom of the apparatus.
Thus, the known apparatus for chlorination of molten magnesium chloride salts fails to provide an adequately complete contact of the melt and the chlorine and, as a result, do not prevent sludge accumulation on the bottom of the apparatus.
Because of an ever increasing demand for magnesium and chlorine a problem arose to improve essentially the apparatus for chlorination of molten salts so as to meet growing requirements of their higher production rate, longer life and lower chlorine consumption.